Actually, I don’t think it’s a bad idea. A large portion of the U.S. is above that latitude (about the 42nd) wherein it spends a large portion of the year with its car windows fully closed. And remember that there are still states without safety inspections. There are still alot of beaters on the road, and I regularly see cars with their mufflers swaying freely beneath the car.
We really don’t have any data suggesting how many people become tired driving as a result of mild carbon monoxide poisoning, only those few that got into spectacular crashes wherein a full investigation was performed…and I wonder how many of those investigations are full enough to cover it. We simply do not know.
It’d be a very inexpensive addition done across a manufacturer’s product line. No more expensive than outside thermometers and rear window defrosters, which even budget cars have now.
The OP may be on to something.